Plutonium is Back on the Menu, Future NASA Missions!

Plutonium dioxide glows with the heat of its natural decay inside a protective cylindrical shell of graphite. (DOE/Idaho National Laboratory)

While I highly advise against humans making a meal out of it (despite my headline) the radioactive element plutonium has long been a staple energy source for many of NASA’s space missions, from Apollo’s ALSEPs to the twin Voyagers to the Curiosity rover.* But the particular non-weapons-grade flavor that NASA needs — plutonium dioxide, aka Pu-238 — has not been in production in the U.S. since the late ’80s; all the Pu-238 since then has been produced by Russia.

That is, until now; researchers at the Department of Energy‘s Oak Ridge National Laboratory (ORNL) in Tennessee have successfully produced the first Pu-238 in the U.S. in 30 years. 50 grams (about one-tenth of a pound) of plutonium dioxide have been manufactured at ORNL, and once the sample has undergone testing to confirm its purity large scale production** will begin.

“This significant achievement by our teammates at DOE signals a new renaissance in the exploration of our solar system,” said John Grunsfeld, associate administrator for NASA’s Science Mission Directorate in Washington. “Radioisotope power systems are a key tool to power the next generation of planetary orbiters, landers and rovers in our quest to unravel the mysteries of the universe.”

Pu-238 is an ideal radioisotope fuel for RPS applications because it generates heat that declines in output by only one half after 88 years. As a result, the ability of an RPS to produce electricity decreases slowly in a highly predictable manner; today the typical RPS is designed for at least 14 years of operation. This allows deep space missions to function for extremely long durations in places where alternatives such as solar panels would be impractical or ineffective. (Source)

*To date 27 NASA missions have used Pu-238 as a power source for electricity and heat.

**”Large-scale production” is a bit misleading; after approval of the first sample only about 300–400 grams (12 oz) will be made and even with new automation implemented only 1.5 kg (3.3 lbs) will be produced yearly. (The Curiosity rover uses 4.8 kg of Pu-238 in its RTG.)

Finally, some sanity! Unfortunately there are loud protests from opponents of space-based nuclear power. This bodes poorly for launching a reactor(s) for the VASIMR engines on the Earth to Mars orbiter and transfer habitat. One of the reactors would be left on the surface to power colony infrastructure construction. The Mars to Earth transfer orbiter returns to Earth for another load… AI robot surveyors and miners anyone?